The Japanese Patent Application Examined Publication (Kokoku) No. HEISEI 7-59927 discloses a method of calculating an ignition timing of an internal-combustion engine (hereinafter referred to as “engine”) immediately after the engine started. According to this method, ignition timing is advanced immediately after the engine started. The ignition timing is shifted to a normal timing when an operational condition parameter reaches a predetermined value.
However, in order to perform so-called FIRE mode for quickly warming up a catalytic converter to bring it active after the engine started, the ignition timing needs to be quickly retarded to raise an exhaust gas temperature. According to the above-disclosed method, the catalyst may not be quickly activated because the retard operation is performed after the ignition timing is advanced and then shifted to the normal ignition timing.
Furthermore, as one approach for controlling an engine, a PI control, a feedback control scheme, is commonly used. According to the PI control, a control input u is obtained according to the following equation (1) where e represents a difference between a desired value and a controlled variable.u=Kpe+KI∫eδτ  (1)
In the equation (1), Kp is a proportional term (P term) and Ki is an integral term (I term). Such control scheme may produce a step in the values of the difference at the start of control or when the desired value is changed. This is because the scheme uses a correction term that reflects the difference between the desired value and the controlled variable. Such a step is not desirable because it may cause a sudden change in the feedback correction amount imposing a significant load to actuators.
Accordingly, it is an objective of the present invention to provide an ignition timing control technique that allows for a quick retard of the ignition timing after the engine starts, raising the exhaust gas temperature and activate the catalyst promptly.